1. Field of The Invention
The present invention relates to a recording-reproducing apparatus, and a recording-reproducing method, capable of high-density recording and also capable of recording and reproducing information in a good reproducibility.
2. Related Background Art
In recent years, uses of memory materials are directed to computers and their related equipment, video disks, digital audio disks, etc., which have been the nucleus of electronic industries, and the development of materials therefor is in very energetic progress. Performances required for the memory materials may vary depending on the uses, but generally include the following:
(1) To have a high density and a large recording capacity.
(2) To have a high recording-reproducing response speed.
(3) To consume a small electric power.
(4To have a high productivity and be inexpensive.
Magnetic memories or semiconductor memories comprised of materials such as magnetic materials or semiconductors have been hitherto chiefly used, but, with recent progress in laser techniques, inexpensive and high-density recording mediums have appeared on the market, which utilize optical memory making use of an organic thin film comprising an organic coloring matter or a photopolymer or the like.
On the other hand, development has been made on a scanning tunnel microscope (hereinafter "STM") capable of directly observing the electron structure of surface atoms of a conductor G. Binning et al, Helvetica Physica Acta, 55, 726 1982)]. which has enabled measurement in a high resolution of real space images regardless of a single-crystalline or amorphous state. Moreover, it has the advantage of the capability of making the observation at a low electric power without giving to the medium any damage that can be caused by currents, and also it can operate in the atmosphere and can be used for various materials. Hence, a wide application is expected in it.
The STM utilizes the mechanism in which a tunnel current flows when a voltage is applied between a metallic probe (a probe electrode) and a conductive substance and both of these are brought close to each other with a distance of about 1 nm. This current is very sensitive to the changes In the distance between the both. The surface structure of the actual space can be drawn by so scanning the probe that the tunnel current can be kept constant, and at the same time a variety of information concerning the total electron clouds of the surface atoms can be read. Here, the resolution power resolving power in the in-plane direction is about 0.1 nm. Hence, the application of the principle of the STM makes it possible to well record and reproduce information in a high density of an atomic order (several A). As recording-reproducing methods used here, Japanese Patent Applications Laid-Open No. 63-161552 and No. 63-161553 propose a method in which the surface state of a suitable recording layer is changed using particle rays (electron rays, ion rays) or high-energy electromagnetic waves such as X-rays and energy rays such as visible light and ultraviolet light, to make a record, which is reproduced using the STM; and a method in which a thin film comprising a material having the memory effect to voltage current switching characteristics, as exemplified by a .pi.-electron organic compound or chalcogen compounds, is used as a recording layer and information is recorded and reproduced using the STM.
It is true that both of these recording-reproducing methods are methods that enable high-density recording making the most of the features of the STM, but such high-density recording greatly depends on the scanning accuracy and positioning accuracy of the probe electrode in the in-plane direction of a recording surface. At present, mechanisms for minutely moving a probe electrode (i.e., micromovement mechanisms) utilize a voltage actuator in which a piezoelectric device is used. There, however, is the problem of the hysterisis of a piezoelectric material, bringing about an obstacle to the achievement of the high-density recording. In addition, the mechanism for the micromovement scanning of the probe electrode in the XY-directions is not necessarily satisfactory in view of the rectangulariry between the X-axis and Y-axis. In other words, there is a problem in the position reproducibility of the micromovement of the probe electrode or scanning mechanisms when information is recorded and reproduced. As a means for solving such a problem, it can be contemplated that a graduation serving as a basis for the position end direction is beforehand marked on a recording medium and the information concerning the position and directionality is detected from such a graduation so that the recording and reproduction are carried out at the position corresponding to the positional information thus detected. Such a method has been firstly employed in recording-reproducing methods of VTR system, as well as in recording systems that are nowadays generally grouped into the high-density recording system, as exemplified by optical disks or optical cards. In such instances, finer positional information must be recorded and detected as a matter of course, with an increase in the density and fineness of recording. Under the present circumstances, however, the fine-processing techniques such as EB drawing and ion beam processing have a limit in the accuracy, of a resolution of 0.01 .mu.m at best. Detection techniques such as the optical heterodyne process also have a limit of a resolution of 0.01 .mu.m. Thus, in the recording and reproduction using the STM, there have been the problems that the accuracy is extremely poor and a complicated process is required for lattice formation.